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Straight line speed with foil boards

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toyletbowl
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Straight line speed with foil boards

Postby toyletbowl » Tue Mar 10, 2015 6:03 am

I hear and read a lot about racing foils and which are the fastest. I'm interested in input on just straight line speed.

I do a fair amount of speed skiing and like riding really fast on kiteboards, but actual find I cannot go into "overdrive" on a foil board when the big gusts hit.

I've only been foiling for 1 year and know riding faster will come with experience, but is it just not possible to "bury the accelerator" when the winds kick in?

It would seem that a properly tuned foil board could actually compete for speed records with the right pilot.

I also know crashes at speed are crazy.

Thoughts?

Thanks,

Bob
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Last edited by toyletbowl on Tue Mar 10, 2015 2:44 pm, edited 1 time in total.

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Peter_Frank
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Re: Straight line speed with foil boards

Postby Peter_Frank » Tue Mar 10, 2015 8:31 am

Some thoughts:

For one, yes it IS possible to just bury the accelerator when the gust kicks in :thumb:

The very best guys go 32-35 knots as max straight line speed on the normal big racefoils.
Where "upwind riding" happens around 15-16 knots for these, when going fast, and you can go a bit higher and only around 13 knots for some.

Seeing these guys go from 12-13 knots and to 35 is insane to watch, awesome acceleration :naughty:

For mere mortals it is different.
When we go 25 knots we feel extremely fast :wink:


There are some issues regarding going faster.

For one it would require a different foil, much smaller wings of course.
But the mast is a major problem - as it has to be stiff and support all load, but when you ride with say a feet of the mast underwater, you get a ridiculously amount of "total loss" drag, thus you have to make a much thinner and smaller lower end of the mast - which is not easy :roll:
The mast does not have a function besides structural support, thus every part of it submerged is wasted drag :(

You cant go fast with your normal hydrofoil, too high drag so not possible to get sufficient pull to go several levels up in speed IMO.
As I assume we are talking 50knots+ here if records ?

The other problem is cavitation of course.

8) PF

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Re: Straight line speed with foil boards

Postby revhed » Tue Mar 10, 2015 10:04 am

Peter_Frank wrote: The mast does not have a function besides structural support
Yaw stability?
Similar to a boat rudder when inputing body twist for yaw change?
When going fast and having the strut at 45° do you not think it is helping hold the T bar in the water as well as acting like a fin to stop downwind sliding similar to a race board fin?
Even though it has a symmetrical profile is there always neutral water force being generated?
I submit that the strut does a lot more than only offer structral support.
R H

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Re: Straight line speed with foil boards

Postby ronnie » Tue Mar 10, 2015 10:20 am

In terms of speed, the designer of Sailrocket started with a blank sheet of paper and designed a vehicle which was going to be the fastest thing on the water - and it's all based around a pulling foil.
That just happens to suit kiting because kites pull. Currently kites are being used mostly with pushing foils, so are limited by the leverage of the rider's weight. With a pulling foil, the power is no longer limited by the weight of the rider, other than how to you handle it when the foil is not pulling.

Sailrocket - max 68.1 knots 500m average 65.45 knots


Kite foiling has a long way to go and may become quite an extreme part of kiting, whereas now it is considered quite serene.

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Re: Straight line speed with foil boards

Postby gmb13 » Tue Mar 10, 2015 1:08 pm

Hi Guys,

If we are talking the 50 knot plus record scene, we must not forget the biggest factor: The rider.

1)Even if the equipment can handle 50 knots, can the rider? The best speed guys are the ones that are a bit insane and have balls of steel and can take the crashes.

2) Besides having a death wish, they need very good control. At those speeds any small mistake proportionally turns into a huge disaster.

Now talking bout getting us normal people who care about not dying to around 40 knots is a different story. Ok. 40 is damn fast and you will blow you ribs out the back of your body if you bail wrong at that speed, but with the right profile and balance if the wings we will get there within the next year, on normal size wings.

On the 2015 generation of foils in flat water most guys are reaching close to 30 knots now and are fairly comfortable holding this speed. And this is still on foils which are not really balanced yet.

Our upwind speeds on normal kites are reaching the average of 20 knots now, even on Tube kites. All this in a fairly short amount of time.

I predict that we will hold the water speed record again within 5 years in open water (like the sail rocket) with foil boards.

--
Gunnar

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Peter_Frank
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Re: Straight line speed with foil boards

Postby Peter_Frank » Tue Mar 10, 2015 3:58 pm

revhed wrote:
Peter_Frank wrote: The mast does not have a function besides structural support
Yaw stability?
Similar to a boat rudder when inputing body twist for yaw change?
When going fast and having the strut at 45° do you not think it is helping hold the T bar in the water as well as acting like a fin to stop downwind sliding similar to a race board fin?
Even though it has a symmetrical profile is there always neutral water force being generated?
I submit that the strut does a lot more than only offer structral support.
R H
Of course the mast CAN be (and is) used for yaw stability, especially if moved further aft, indeed.

But if you could remove the mast fully, and use a vertical stabiliser (or fuselage height) or up/downswept horisontal stabilizer instead, you can obtain the same yaw stability with a lot less drag (less area needed) I would say :D

Most likely not just as simple, as you NEED this structural support, no matter what, and besides can the dynamic behaviour be changed too much (rider input response, turns etc).

And no, I dont think the mast acts much as a lifting device, maybe not at all, when you angle the board a lot.
You will have a huge, in fact 71% of the wing lift acting as a force lifting "up", when angled 45 degree to windward, even if you had no mast !
And a hydrofoil in balance would not need any lift from the mast - if so, it would be really slow as the fuselage and rudder will increase drag hugely.
I might be corrected in this, if tests shows otherwise, but till then this is my belief :thumb:

8) PF

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Re: Straight line speed with foil boards

Postby toyletbowl » Sun Mar 15, 2015 5:59 pm

Perfect.....pretty much as I thought on trying to bury the peddle for max speed.

1st....need huge balls
2nd....more experience.
3rd.....fast foil.
4th.....line mounted go pro to document the massive crashes.

Bob
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Re: Straight line speed with foil boards

Postby tkettlepoint » Sun Mar 15, 2015 9:09 pm

Bob I am with you...
if you are willing so am I..



terrie
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